Pressure gauges are widely utilized in a myriad of different environments for commercial and industrial applications where measuring and indication of fluid pressure values is required. Depending on the instrument, values of pressure can be displayed in either digital or analog form. The primary sensing element of the gauge typically comprises a Bourdon tube having a free end that incurs a predictable displacement in response to pressure changes to which it is exposed. Typically, tube displacement is translated via a movement or amplifier to a rotatable pointer that is displaced opposite a dial of calibrated pressure values.
It can be appreciated that if and when an overpressure is encountered within the Bourdon tube it could, if of sufficient magnitude, cause the Bourdon tube to burst with the potential for exploding and throwing the case and/or lens. Needless to say, explosions of this type can prove hazardous, particularly to any bystander in the vicinity of the gauge.
A current standard of Underwriter's Laboratories, Inc., UL252A relates to "Compressed Gas Regulator Accessories". The standard establishes the requirement that all components of a compressed gas regulator assembly including the pressure gauge operate at a selected maximum pressure of between 30-300 psig. Each gauge, whether of 30 psi max or 300 psi max. must be capable of withstanding a pressure five times its maximum operating pressure. At or above the five times multiple, the accessory shall either retain or release the pressure without rupture or throwing of parts. Burst pressures for a Bourdon tube can typically vary from about 1100 psi for a 30 psi max. gauge to 5,000 psi for a 300 psi max. gauge.
Various approaches for compliance with the above U.L. standard have included a perforator within the tube that punctures a hole in the tube in the course of deformation. Another approach has been to utilize conventional rear venting of the case to supposedly prevent injury in the vicinity of the gauge.
While operative, none of the above have been found sufficiently practical for an inexpensive pressure gauge and despite reccognition thereof, a ready solution has not heretofore been known.